Why Rhododendrons Require a Mulch
by G. G. Nearing, Ramsey, N.J.
A study recently published to prove that azaleas, under certain circumstances, can benefit by having the mulch removed in autumn, may do incalculable harm if rhododendron enthusiasts try to adapt it to the ordinary planting of residential grounds. The authors of this study made clear that it was intended only for nurseries, but this fact may easily escape the average reader. Also the benefits described were the lessening of frost injuries to semi-hardy azaleas--nothing else.
In nurseries most plants are held in a state of suspense between transplanting, and cannot be given the ideal conditions under which they should flourish for the eventual owner. Nurserymen hate mulch. Not only would the expense of permanently mulched planting be prohibitive in the average nursery, but its benefits would not materialize, because any plant may at any moment require to be moved again. Mulch is a great nuisance in moving, and works into the soil, where it does not belong.
The whole idea of mulching depends on permanence. No matter how carefully the work of transplanting is carried out, more than a year is required in the new situation before any rhododendron can regain the full vigor of health and growth.
The root system of a rhododendron is entirely unlike that of an apple tree, or of almost any tree or shrub that does not belong to the Heath Family. The apple tree puts out sturdy root shoots ranging wide and deep, able to penetrate hard soil, even sometimes rock, by an amazing display of strength. The absorption of crude sap is performed not by these powerful leaders, but by root-hairs along the sides of the lesser tips. Rhododendrons have no root-hairs, and the extremely delicate, thread-like absorbing roots do not range far, but are massed in immense numbers near the soil surface and no farther from the trunk than the average branches spread. These roots do not and cannot penetrate hard soil, nor can they reach depths to replenish lost moisture. Therefore the surface where they grow must be always moist, always protected from drying wind and sun, always insulated against heat and cold, always dark. One single hour of exposure by removal of the mulch will kill off these essential roots, and even though the mulch is replaced the same clay, that plant cannot regain full vigor for many months or years.
Rhododendrons injured do not die, at least not for a long while, but many of their leaves drop off, the lower branches die, and they tend to become ugly sticks with tufts of foliage at the top. Whenever you see an unsightly one of this type, you may be sure the mulch has been removed. If the mulch is returned and kept permanently in place, new lower branches will begin to grow within a year or two, and eventually the plant can be restored to health.
A mulch of peat, sawdust or hay is little better than no mulch at all. There are no proper air-spaces for insulation. In the case of peat, the roots grow up very rapidly to the upper surface of the peat, and there demand to be properly mulched, or they will suffer from heat, cold and drought. Peat has the additional fault that it freezes more quickly and stays frozen longer than almost any other familiar substance.
Advertising has recently built up in the mind of the average planter, an emphasis on chemical reactions which almost excludes nature. The reader of such nonsense is tempted to think that you put so much of this chemical with so much of that, and you get a rhododendron. You don't. Chemistry has a little something to do with plant growth, but not much.
For millions of years trees have stood together in forests, and their falling leaves have accumulated from year to year. Some of these leaves rot away in a single season, while others require two or three years. Go into the woods with a knife and cut down through the natural accumulation. At the top will be comparatively un-decayed leaf material, with plenty of air spaces between the individual leaves where they curl or where twigs intervene. Lower you will find the leaves softened by decay and largely matted together. Still lower they merge into a dark, crumbly mass, and into the soil itself. Everywhere in the woods, this condition tends to be the same.
For millions of years, rhododendrons have learned how to adapt themselves to this condition, spreading a mat of thread-like roots just where the leaves are becoming soil. During those millions of years, nobody went around raking the leaves away-nobody roamed there with bags of chemicals to destroy the ideal conditions of the virgin forest. The rhododendrons cannot change their nature overnight. If you want them to thrive, give them as nearly as possible the conditions under which they evolved during those millions of years, and let them alone.
The entire story is not told until you realize that billions of living organisms are involved in every square foot of the mulch. Insects, worms, fungi and-most important of all-many kinds of bacteria are furiously busy working in the leaves and in the newly formed soil. Once the conditions under which they thrive are altered, they, like the rhododendrons, tend to flag and die, and of course if you poison them, the end comes more swiftly. They work day and night to keep your rhododendrons in health, though of course they don't know that is what they are doing. You have billions of laborers working for you without pay. Why kill them?
When you transplant and mulch a rhododendron, no matter how carefully, you cannot reproduce exactly the conditions under which it was growing when you dug it. To organize the mulch into the necessary layers, with all the little creatures doing the right thing in the right place at the right time, is at first impossible. But if you do your best and then let nature take over without disturbance or interference, everything will gradually right itself. In a year or so your rhododendrons will begin to thrive gloriously. That is the secret. There is no other way.